Driver board control system for modular conveyor with address-based network for inter-conveyer communication

ABSTRACT

A method and control system are provided for controlling a modular conveyor system, which may be networked together with other such systems in order to implement a control strategy for a modular conveyor system. The control system comprises a communications port for interconnection of the control system with a network for sending outgoing addressed data to other devices on the address-based network and for receiving incoming addressed data from other devices. The control system further comprises a logic system, which may receive a signal from an object sensor and provide a control signal or output adapted to control activation of a motorized roller assembly, based on an input signal from the object sensor or the communications port. The logic system may provide for single step operation whereby system troubleshooting may be facilitated, and in addition may provide situation aware and output value source selection functionality.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/768, 494, filed Jan. 30, 2004, entitled, DRIVER BOARD CONTROL SYSTEMFOR MODULAR CONVEYOR WITH ADDRESS-BASED NETWORK FOR INTER-CONVEYERCOMMUNICATION, which is a continuation of U.S. patent application Ser.No. 10/309,400, filed on Dec. 3, 2002, entitled DRIVER BOARD CONTROLSYSTEM FOR MODULAR CONVEYOR WITH ADDRESS-BASED NETWORK FORINTER-CONVEYER COMMUNICATION, which is a continuation of U.S. patentapplication Ser. No. 09/729,486 filed on Dec. 4, 2000, entitled DRIVERBOARD CONTROL SYSTEM FOR MODULAR CONVEYOR WITH ADDRESS-BASED NETWORK FORINTER-CONVEYOR COMMUNICATION, which is a continuation-in-part ofco-pending U.S. patent application Ser. No. 09/559,625 filed Apr. 27,2000; Ser. No. 09/574,982 filed May 19, 2000; Ser. No. 09/644,635 filedAug. 23, 2000; and Ser. No. 09/669,822 filed Sep. 26, 2000, theentireties of all such applications of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to the art of industrial controllers, andmore particularly to systems and methods for controlling a modularconveyor.

BACKGROUND OF THE INVENTION

Industrial controllers are special purpose computers used forcontrolling industrial processes, manufacturing equipment, and otherfactory automation, such as conveyor systems. In accordance with acontrol program, the industrial controller measures one or more processvariable or inputs reflecting the status of a controlled conveyorsystem, and changes outputs effecting control of the conveyor system.The inputs and outputs may be binary, (e.g., on or off), as well asanalog inputs and outputs assuming a continuous range of values. Thecontrol program may be executed in a series of execution cycles withbatch processing capabilities.

The measured inputs received from a conveyor system and the outputstransmitted to the conveyor system generally pass through one or moreinput/output (I/O) modules. These I/O modules serve as an electricalinterface between the controller and the conveyor system, and may belocated proximate or remote from the controller. The inputs and outputsmay be recorded in an I/O table in processor memory. Input values may beasynchronously read from the controlled conveyor system by one or moreinput modules and output values are written directly to the I/O table bythe processor for subsequent communication to the conveyor system byspecialized communications circuitry. An output module may interfacedirectly with a conveyor system, by providing an output from an I/Otable to an actuator such as a motor, valve, solenoid, and the like.

During execution of the control program, values of the inputs andoutputs exchanged with the conveyor system may pass through the I/Otable. The values of inputs in the I/O table are asynchronously updatedfrom the controlled conveyor system by dedicated scanning circuitry.This scanning circuitry may communicate with input modules over a bus ona backplane or network communications. The scanning circuitry alsoasynchronously writes values of the outputs in the I/O table to thecontrolled conveyor system. The output values from the I/O table arethen communicated to one or more output modules for interfacing theconveyor system. Thus, the processor may simply access the I/O tablerather than needing to communicate directly with the conveyor system.

An industrial controller may be customized to the particular process bywriting control software that may be stored in the controller's memoryand/or by changing the hardware configuration of the controller to matchthe control task. Controller hardware configuration is facilitated byseparating the industrial controller into a number of control modules,each of which is performing a different function. Particular controlmodules needed for the control task may then be connected together on acommon backplane within a rack. The control modules may includeprocessors, power supplies, network communication modules, and I/Omodules exchanging input and output signals directly with the controlledconveyor system. Data may be exchanged between modules using a backplanecommunications bus, which may be serial or parallel. A typical hardwaremodification may involve adding additional I/O modules in order to beable to control additional equipment.

Various control modules of the industrial controller may be spatiallydistributed along a common communication link in several racks. CertainI/O modules may thus be located in close proximity to a portion of thecontrol equipment, and away from the remainder of the controller. Datais communicated with these remote modules over a common communicationlink, or network, wherein all modules on the network communicate using astandard communications protocol.

In a typical distributed control system, one or more output modules areprovided for interfacing with a process. The outputs derive theircontrol or output values in the form of a message from a master or peerdevice over a network or a backplane. For example, an output module mayreceive an output value from a processor, such as a programmable logiccontroller (PLC), via a communications network or a backplanecommunications bus. The desired output value is generally sent to theoutput module in a message, such as an explicit message or an I/Omessage. The output module receiving such a message will provide acorresponding output (analog or digital) to the controlled process.

Control systems are often employed in association with conveyor systemsfor moving objects along guided tracks, including modular conveyorsections or “sticks”. Conveyor systems for moving objects betweenstations in a manufacturing environment or for accumulating anddistributing products in a warehouse operation are well known in theart. Such conveyor systems provide upwardly exposed conveying surfaces,such as rollers, positioned between guiding side rails. The rollers arepowered by controllable motors to move objects placed on top of themalong a track defined by the rails.

Assembly of conveyor systems is facilitated by the use of “conveyorsticks” which may include one or more short sections of rollers andguide rails, which are connected together to form the final conveyorsystem. The conveying surface of each conveyor stick may be broken upinto one or more zones, each associated with a sensor for detecting thepresence of an object on the conveyor at the zone. A control circuitcommunicates with each zone and sensor via a number of cables to controlthe zones, in order to accomplish a number of standardized tasks.

Such conveyor systems may be adapted to perform one or more tasks oroperations. One such task is that of “accumulation” in which a controlcircuit for a given zone operates its rollers when the sensor, in anupstream zone, indicates an object is at that zone and the sensor of a“downstream” zone indicates that no object is in that downstream zone.This logic causes the conveyor zones to move objects along to fill allzones with objects. In a “slug release” operation, each control circuitin a defined release zone operates its rollers if its sensor indicatesan object is present and no object is in the downstream zone from thedefined release zone. This logic causes the emptying of a predefinedsection of the conveyor, typically to a downstream portion. A third modeof operation is “singulation release” in which a single object at a timeis unloaded from the conveyor system. Each upstream control circuitoperates its rollers to move its objects downstream one zone.

In order to perform these tasks, the control circuit for a particularconveyor stick may communicate in a limited fashion with the controlcircuits (or at least the sensors) of associated upstream and downstreamconveyor sticks. This may be accomplished via cabling between controlcards or sensors of the conveyor sticks, typically within one of theside rails. The conveyor system may operate without the need for acentral controller, for example, such as where one or more I/O pointsare provided for each zone, thus reducing the wiring associatedtherewith. By eliminating the need for such wiring, the conveyor stickscan be easily assembled or reconfigured. Nevertheless, the lack ofcentral control makes the conveyor system relatively hard to reconfigurerequiring, for example, settings to being manually adjusted on eachcontroller board when delay times and conveyor speeds are changed.Further, lack of centralized communication between components of theconveyor system makes it difficult to detect and report conveyor systemproblems such as motor failure or material jamming.

Some conventional control devices and systems for such conveyor systemsprovide outputs solely based on messages from a network, having nointernal logic. For example, such a device may provide an outputaccording to an output value received in an I/O message from a master(e.g., a PLC), and may maintain that value during normal operation untilanother message is received. In some such devices, certain conditionscan affect the output value. For instance, when a module detects acommunications fault, the output may go to a known state. However, thereare many sources that may affect an output point's value. These includean I/O message, an explicit message, local logic, fault or idle values,and/or a forcing message. Heretofore, the source of an output value wasdetermined according to fixed controller architecture constraints. Thus,a user had limited ability to decide priorities for the source of aconveyor system output module's output value. In addition, there aremany conditions or events associated with conveyor systems for which itmay be desirable to provide another output value to the device.Heretofore, a user had no ability or a limited ability to define outputdevice behavior in lieu of regular I/O messages.

In addition, some conventional conveyor control devices provide a runmode wherein a module executes a control program and a configure modewherein the control program execution is suspended. As conveyor controlsystems become more widely distributed, the logic or control programassociated with a particular system may be executed on a large number ofmodules or devices. In this way, individual processors in the devicesexecute a program autonomously from the rest of the system components.Smart devices, such as I/O modules, transducers, sensors, valves, andthe like may thus be programmed to execute certain logical or otherprograms or operations independently from other such devices.

The distribution of smart devices in a networked conveyor control systemhas many advantages. However, system testing and troubleshooting areoften more difficult in distributed systems. In a system with manyautonomous smart devices, each having its own control logic or program,problems in system performance cannot easily be traced to a specificdevice. Once the component devices in such a system are placed intoexecute or run mode, the logic or control programs associated therewithrun independently, and are often not synchronized. Even where certainconveyor control devices in a system are synchronized to certain events,determining the source of a system control problem is still difficult.

In many cases, the source of a control problem is an error inprogramming a particular module. For example, the logic function in aparticular module may be the function of several input values or states.Problems in the logic function may only be discernable in one or a smallnumber of input combinations. In widely distributed conveyor controlsystem architectures, system events occur asynchronously, such as I/Ovalue state changes, messages, etc. Thus, when a problem occurs, it maybe difficult to determine the source of the error.

This is particularly problematic in system startup situations. Largeconveyor control systems are typically tested before application to areal process, with inputs simulated and outputs tested under a varietyof input conditions. In addition, control system diagnostics are neededin the field, when problems in system performance are recognized, orwhen system parameters are changed. Present diagnostic tools aretypically limited to simulating input signals and monitoring outputvalues. Conventional control devices do not provide for ease oftroubleshooting in such distributed conveyor control systemapplications.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order toprovide a basic understanding of some aspects of the invention. Thissummary is not an extensive overview of the invention. It is intended toneither identify key or critical elements of the invention nor delineatethe scope of the invention. Its sole purpose is to present some conceptsof the invention in a simplified form as a prelude to the more detaileddescription that is presented later.

The present invention provides a conveyor control system, which may benetworked together with other such systems in order to implement acontrol strategy for a modular conveyor system. An address-based networkconnects control components within conveyor sticks together allowingcontrol, monitoring or configuration of the components within theconveyor sticks from a central device. The control system according tothe invention may further be adapted to perform self-configuration,whereby individual control systems may configure themselves on power upin order to communicate with one or more adjacent or related controlsystems, in order to effectuate a control strategy for the conveyorsystem. The conveyor control system may also be employed in non-modularor continuous conveyor systems in accordance with the invention.

The conveyor sections may comprise separated upstream and downstreamends having mechanical connectors for connecting to downstream andupstream ends, respectively, of other conveyor sections. The conveyorsections support motorized roller assemblies and associated objectsensors sensing objects on the conveyor section. A communications portin the individual control systems provides for interconnection of thecontrol system with the address-based network for sending outgoingaddressed data to other devices on the address-based network and forreceiving incoming addressed data from other devices. Moreover, thecontrol system communications ports may provide for sending andreceiving broadcast messages as well as individually addressed messages,for example, wherein a control system may send a universal broadcastmessage to all devices on the network.

The control system further comprises a logic system communicating withor being part of the communications port, which may receive a signalfrom an object sensor and provide a control signal or output adapted tocontrol activation of a motorized roller assembly, based on an inputsignal from the object sensor or the communications port. For example,an external object presence signal associated with at least one of theother conveyor sections or another component within a conveyor sectionmay be received by the communications port from the address-basednetwork. The invention further contemplates control systems having alogic system, where the control system provides a sensor functionality,whereby the presence of an object is sensed, and a signal or message isprovided to the address-based network. Accordingly, the logic system mayfurther transmit an object presence signal as outgoing addressed (e.g.,or broadcast) data through the communications port, independent ofwhether an output or control signal is provided by the control system.The logic system may be further adapted to perform situation-awareconfiguration and execution functions and output value source selectionfunctions in order to reduce or minimize the above-mentionedshortcomings in conventional conveyor controls, and/or may supportsingle-stepped or strobed synchronization to facilitate conveyor systemsetup and diagnostics. It will be appreciated that the strobedsynchronization or single-step mode of operating the control system maybe employed in addition to communications protocols wherein a masterdevice sends a strobe or broadcast message to a plurality of slavedevices on a network, to which slaves may then respond one after anotheraccording to their individual network address settings, which issometimes referred to as strobed communications. In this regard, themethods and systems of the present invention find application inassociation with numerous communications protocols, including polledcommunications, strobed or broadcast communications, and others, and itwill be understood that such communications protocols fall within thescope of the present invention. The logic system, moreover, may compriseseparate program attributes for different drive roller products made bydifferent vendors.

In accordance with one aspect of the invention, there is provided acontrol system for a modular conveyor, such as a conveyor having amotorized roller for moving objects on the modular conveyor and anobject sensor for sensing objects on the modular conveyor. The controlsystem comprises a drive controller adapted to control a motorizedroller in the modular conveyor, a communications port adapted to connectthe control system to an address-based network, to send outgoingaddressed data to other devices in the address-based network, and toreceive incoming addressed data from the address-based network. Thecontrol system further comprises a logic system adapted to receive aninput signal from either the object sensor or the communications port orboth, and to provide a roller control signal to the motorized rolleraccording to the input signal.

In accordance with another aspect of the invention, the logic system maycomprise an output module, which includes a value source selectoradapted to receive messages from the address-based network, and a locallogic function associated with the value source selector to create abinding and providing a signal thereto. The logic function may furtherinclude an output receiving an output value from the value sourceselector based on the signal from the local logic function, and havingan output signal. The value source selector may be adapted toselectively ignore I/O and explicit messages from the address-basednetwork based on the binding and to selectively use an idle action andset the output value according to an idle value when the local logicfunction is disabled. In addition, the value source selector mayselectively use a fault action and set the output value according to afault value based on an override attribute, and selectively ignore idlemessages according to the override attribute.

According to yet another aspect of the present invention, the logicsystem may comprise an output providing an output signal according to anoutput value, an indicator adapted to receive message information fromthe communications port and providing indicator data, and a logic unit,which receives message information from the communications port andindicator data from the indicator. The logic unit is adapted to performa logic function, and to selectively provide the output value to theoutput according to the message information or the logic function.

The logic unit may thus take into account indicator data in determiningthe output value, which was possible in previous conveyor controllers.For example, the indicator data may include an I/O connection healthindicator, a messaging connection health indicator, an I/O connectionerror indicator, a run event indicator, and idle event indicator, anetwork error indicator, an I/O point fault indicator, a hardware inputindicator, a hardware output indicator, and I/O data. The control systemthus allows a user to define both the status/event indicators which willbe considered, as well as the decisional logic used in providing anoutput value to the output of the device. The logic unit, for example,may comprise a processor or other logic device, which may be configuredby a user to perform various functions, such as boolean operations,flip-flops, counters, and/or timers.

In accordance with still another aspect of the invention, a user mayplace one or more conveyor control systems or devices into a step mode,wherein the control systems are adapted to execute a specified number ofiterations of their internal logic or control programs, or execute suchprograms for a specified time period, and then stop or suspendexecution. The user may then perform system diagnostics, for example, byinterrogating certain conveyor section controllers to obtain statusinformation, output and input values, and the like. The system may thenbe further iterated and the process repeated, in order to enable theidentification of logic programming and/or hardware problems in asystem. In this regard, the logic system may be adapted to execute astored program and to receive a message from a master device via thecommunications port, wherein the message comprises a parameter. Thelogic system is further adapted to execute at least a portion of thestored program according to the parameter and to subsequently suspendexecution of the stored program according to the parameter. Theinvention thereby provides significantly improved diagnostic andtroubleshooting capabilities over conventional conveyor control systemsand devices.

According to another aspect of the invention, a method is provided forcontrolling a modular conveyor system. The method may be implemented,for example, in a modular conveyor control system having a drivecontroller adapted to control a motorized roller as well as acommunications port adapted to connect the control system to anaddress-based network. The method comprises providing a logic system inthe control system, receiving an input signal from an object sensorassociated with the modular conveyor or from the communications port,and providing a roller control signal to the motorized roller accordingto the input signal.

According to yet another aspect of the invention, the logic systemcomprises an output device adapted to provide an output according to anoutput value, wherein the method may further comprise associating theoutput device with a logic function, providing the output valueaccording to the logic function, and ignoring explicit messages from theaddress-based network. In this regard, the method may further includeignoring value messages from the address-based network, selectivelyignoring fault messages according to an override attribute, andselectively ignoring idle messages according to the override attribute.

According to another aspect of the invention, the logic system maycomprise an output device having a device status, wherein the methodfurther comprises associating the output device with a logic function incommunication with the address-based network, and associating the logicfunction with an indicator. In addition, the method may includereceiving a status message from the address-based network, receiving avalue message from the address-based network, updating the indicatoraccording to the status message and the device status, and selectivelyproviding an output value to the output device from one of the logicfunction and the value message, according to the logic function.

According to still another aspect of the invention, the control systemmay be adapted to perform self-configuration. Thus, a control system maycomprise a network address, which may be used to pre-configure links orassociations with other related control systems in the conveyor system.For instance, each control system may automatically configure networklinks to send and/or receive information from adjacent (e.g., upstreamand down-stream) or related control systems, in order to implement oneor more particular control strategies associated with operation of theconveyor system.

This feature facilitates ease of setup of new conveyor systems as wellas reconfiguration of existing systems, whereby manual reprogramming ofindividual control systems is minimized or reduced. For example, thecontrol system having an address N may be configured on power up toreceive a message from a system at address N−1 to indicate the presence(e.g., or absence) of an object in an up-stream conveyor section.Similarly, the control system (e.g., at address N) may further beautomatically configured to provide a message to a down-stream conveyorsection (e.g., at address N+1) indicating the presence of an object inthe current conveyor section.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described. The followingdescription and the annexed drawings set forth in detail certainillustrative aspects and implementations of the invention. However,these implementations are indicative of but a few of the various ways inwhich the principles of the invention may be employed. Other aspects,advantages and novel features of the invention will become apparent fromthe following detailed description of the invention when considered inconjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary multi-bank conveyor systemmade up of a variety of modular conveyor sticks, the banks havingcontinuous network cables attached at one end to a central industrialcontroller;

FIG. 2 is a top plan view of an exemplary conveyor stick of FIG. 1showing its division into zones, each with a plurality of controlsystems, motors and sensors in accordance with the invention, whereinthe control systems are connected together by a shared network cablesection having connectors at upstream and downstream ends;

FIG. 3 is a side elevation view of the exemplary conveyor stick of FIG.2;

FIG. 4 is a detailed perspective view of the upstream end of theconveyor stick of FIGS. 2 and 3 illustrating connection of sharednetwork cable sections between connected conveyor sections to form acontinuous shared network cable;

FIG. 5 is a side elevation view of an exemplary control system inaccordance with an aspect of the invention, having a detachablecommunication port for receiving a shared network cable section andproviding control logic for an associated zone of the conveyor stick;

FIG. 6 is a figure similar to that of FIG. 3 showing an alternativewiring method using a semi-continuous network cable “daisy chained”along the rails of the conveyor sticks;

FIG. 7 is a schematic illustration of an exemplary control system forcontrolling a modular conveyor according to various aspects of thepresent invention;

FIG. 8 is a flow diagram schematically illustrating a method forselecting an output value for an output device or module which may beimplemented in a conveyor control system in accordance with theinvention;

FIG. 9 is a schematic diagram illustrating aspects of an exemplary logicsystem for selecting an output value for an output device or module in aconveyor control system according to the invention;

FIG. 10 is a schematic diagram illustrating a control system includingthe method and system for selecting an output value for an output deviceor module according to the invention;

FIG. 11 is a schematic diagram illustrating an output device or modulein which the methods and systems of the present invention may beimplemented in a modular conveyor system;

FIG. 12 is a schematic diagram illustrating user-defined attributes inaccordance with the invention;

FIG. 13 is a flow diagram illustrating an exemplary method of providingan output value for an output device in a conveyor control system inaccordance with the present invention;

FIG. 14 is a schematic diagram illustrating an exemplary output devicefor a conveyor control system in accordance with another aspect of theinvention;

FIG. 15 is a schematic diagram illustrating another exemplary outputdevice in accordance with the invention;

FIG. 16 is a schematic diagram illustrating an exemplary configurationof a conveyor control system output device in accordance with anotheraspect of the invention;

FIG. 17 is a schematic diagram illustrating another exemplaryconfiguration of a conveyor control system output device in accordancewith the invention;

FIG. 18 is a schematic diagram illustrating an exemplary control systemincluding an output device in accordance with the invention;

FIG. 19 is a schematic block diagram illustrating an exemplarydistributed conveyor control system in which various aspects of thepresent invention may be implemented;

FIG. 20 is a block diagram illustrating an exemplary mode change messagein accordance with the invention;

FIG. 21 is a block diagram illustrating an exemplary step commandmessage in accordance with the invention;

FIG. 22 is a block diagram illustrating another exemplary mode changemessage in accordance with the invention;

FIG. 23 is a flow diagram illustrating an exemplary method of performinga function in a conveyor control system in accordance with theinvention;

FIG. 24 is a flow diagram illustrating further aspects of the method ofFIG. 23;

FIG. 25 is a block diagram illustrating an exemplary step parametermessage in accordance with the invention;

FIG. 26 is a block diagram illustrating another exemplary step commandmessage in accordance with the invention;

FIG. 27 is a flow diagram illustrating another exemplary method ofperforming a function in a conveyor control system in accordance withthe invention;

FIG. 28 is a flow diagram illustrating further aspects of the method ofFIG. 27; and

FIG. 29 is a flow diagram illustrating further aspects of the method ofFIGS. 27 and 28.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is now described with reference to the drawings,wherein like reference numerals are used to refer to like elementsthroughout. In order to provide context for the various features andaspects of the present invention, an exemplary conveyor system isillustrated and described. Referring now to FIG. 1, an exemplaryconveyor system 10 may be assembled from a plurality of conveyor sticks12, each providing upwardly exposed rollers 14 for moving one or moreobjects 16 along a conveyor axis 18. The rollers 14 of the conveyorsticks 12 may be reversible, thus allowing the object 16 to be moved ineither direction along axis 18 in a controlled fashion. Nevertheless, anarbitrary “upstream” end 20 and “downstream” end 22 may be defined foreach conveyor section representing one direction of flow along axis 18for the processes of accumulation and slug release.

The conveyor sticks 12 may be arranged in one or more parallel banks 24and may include alternative conveyor sticks 26 having diverter branches28 providing a bifurcated path splitting a single upstream bank 27 intomultiple downstream banks 24. The diverter conveyor sticks 26 mayinclude a movable wall (not shown), which pushes packages either to theleft or to the right. As depicted at an upstream end 20 of the banks 24,a continuous network cable 30 may connect each bank 24 (e.g., upstreamends 20 of one bank 24 to the downstream ends 22 of a next bank 24) to acentral programmable logic controller (e.g., PLC) 34 also as known inthe art.

The network cable 30 provides for communication of data in packetshaving associated addresses identifying the destination and/or source ofthe data of the packet. This addressing allows the conductor of thenetwork cable 30 to be shared among many devices while data maynevertheless be directed to or otherwise associated with particular onesof those devices. In this regard, a destination address may be linked tothe packet indicating the device for which the data is intended.Alternatively or in combination, a source address may be attached to thepacket and the device for which it is intended may have a stored tableof addresses from which it will receive such packets. Broadcastingprotocols may also be implemented on the network cable 30. The DeviceNetstandard based on the CAN controller protocol may be suitable for thispurpose but other network protocols may be used alternatively or incombination. For example, a network cable 30 for the DeviceNet standardemploys four conductors, two for supporting data communication and twofor providing power.

Referring now to FIGS. 2 and 3, a single conveyor stick 12 divides itsrollers 14 into multiple zones 36. Thus, for example, a conveyor stick12 having a length between its upstream end 20 and its downstream end 22over ten feet, may include four, 2.5 foot zones 36, each with multiplerollers 14. Each zone 36 may include one motorized roller assembly 38,for example, those having an internal motor mechanism of a type wellknown in the art. This motorized roller assembly 38 communicates itsmotion by means of belts 40 with the other rollers 14 of the zone 36.Positioned at a downstream end of each zone is a sensor 42 such as mayreceive a light beam (not shown) from an emitter (not shown), the beamcrossing the upper surface of the last roller 14 of the zone 36 at itsdownstream side in a direction substantially perpendicular to theconveyor axis 18. An object (e.g., object 16) breaking the light beam,signals the presence of an object at the zone.

For each zone 36, a controller card or control system 48 communicateswith the sensor 42 and with the motorized roller assembly 38 to providecontrol functions as will be described. Each control system 48 alsocommunicates in shared fashion with a cable section 31. The cablesection 31 runs in “daisy-chain” fashion connecting to each of controlsystems 48 of the conveyor stick 12, each control system 48communicating with rollers and sensors of their respective zones 36. Thediverter conveyor stick 26 of FIG. 1 may comprise a control system 48(not shown) and thus may be easily integrated into the rest of theoperation of the conveyor system 10. It will be appreciated thatalthough the exemplary control system 48 is illustrated and describedhereinafter with respect to modular conveyor systems, that the controlsystem 48 may alternatively or in combination be employed in associationwith other (e.g., non-modular or continuous) conveyor systems inaccordance with the present invention. Referring also to FIGS. 4-6, oneimplementation of the control system 48 provides for control leads 62leading to the sensor 42 and power leads 64 leading to the motorizedroller assembly 38. The control system 48 may comprise level shiftingand power circuitry for supporting the motorized roller assembly 38 andthe sensor 42. Separated power leads 65 provide power that may beswitched by the control systems 48 directly to motors of the motorizedroller assemblies 38. A connector 66 is provided to receive a networkcard 68, which attaches to the network cable and provides the necessaryprotocol for communication on the network cable 30. Other aspects of thecontrol system 48 will be illustrated and described in greater detailhereinafter. The control systems 48 may be held by side panels 50 of theconveyor stick 12 which may further serve to support the rollers 14. Theside panels 50 provide integral cable raceways 52 into which the controlsystems 48 may fit as well as the cable section 31. Cable section 31terminates in connectors 54 at its upstream and down stream endsadjacent to the upstream and downstream ends of one of the side panels50.

Referring now to FIG. 4, the side panels 50 terminate at their upstreamand downstream ends 20 and 22 at a mechanical connector 56 beinggenerally a plate perpendicular to the conveyor axis 18 and includingtwo axial holes 58. The mechanical connector 56 and its axial holes 58match with corresponding mechanical connectors 56′ and holes 58′ of anadjacent conveyor stick 12′. Fasteners 60 inserted through these holes58′ and 58 allow assembly of the conveyor sticks 12 together into aconveyor system 10. A notch 61 in the mechanical connector 56 permitspassage of either cable section 31′ into the raceway 52 or cable section31 into the raceway 52′ where they may be attached to each other viaelectrical connectors 54. A small amount of additional slack is providedin the cable sections 31 and 31′ to permit this operation whilepreserving complete enclosure of the network cable 30 (made up of cablesections 31) within the raceway 52 or 52′. Thus, assembly of conveyorsticks 12 into a conveyor system 10 is a simple matter of joiningmechanical connectors 56′ and electrical connectors 54 of each newconveyor stick as it is added.

Referring to FIG. 5, the network card 68 may comprise an address switch70 for setting a “media access layer” address of the control system 48so that data sent on the network 30 by different devices (e.g., controlsystems 48 and/or central controller 34) may be distinguished. Before orat the time each conveyor stick 12 is added to the conveyor system 10,its control systems 48 may be given a unique address via the switches70. Alternatively or in combination, the network address of the controlsystem 48 may be programmed via messaging from the network 30. Where theaddress space (e.g., the total number of unique addresses allowed by thenetwork) is limited to a number less than the total number of controlsystems 48, a bridge 32 (e.g., FIG. 1) may be connected betweendifferent groupings of the conveyor sticks 12. In this manner, anexpansion may be provided of the addresses that may intercommunicate, aswill be described further below.

During operation of the exemplary conveyor system 10, each controlsystem 48 may receive data from the central controller 34. The controlsystems 48 may further provide data to the central controller 34 uponrequest from the central controller 34, for example, under a simpledirector/follower protocol. The network card 68 will decode only thosemessages addressed to it according to low level procedures well known inthe art.

All pertinent data necessary for control of the conveyor stick may bedownloaded from the central controller 34 to the control systems 48including, for example, the desired motor speed and/or direction for themotorized roller assembly 38 and delay times between actuations of themotorized roller assembly 38 and changes of state of the sensor 42.Commands such as for accumulation, singulation release and slug releasecan be issued from a central location or from local switches oncontrollers also attached to the network cable 30. Likewise data fromthe control system 48 may be relayed to the central controller 34including indications of jamming, the state of the sensor 42, the stateof the motorized roller assembly 38, the temperature of the motorizedroller assembly 38, current draw of the motor, etc. This information, asuploaded to central controller 34, may provide a centralized picture ofthe operation of the conveyor system 10.

In addition, the central controller 34 may manage the interconnection ofthe control systems 48 with its adjacent zones in its conveyor stick 12,or in upstream or downstream conveyor sticks 12, by providing eachcontrol system 48 with the address of other control systems 48associated with its upstream and downstream zones from which or to whichsensor data may be sent. In another aspect of the invention, the controlsystems 48 may automatically configure themselves upon power up to sendand receive such information from one or more other adjacent orotherwise associated control systems 48, for example, based on thenetwork address setting (e.g., address switch 70). The provision of theaddress-based network 30 facilitates this self-configuration, andfurther provides for elimination of the dedicated wiring betweenconventional conveyor controllers heretofore required to implementinformation sharing between conveyor sections or zones. Further,reconfiguration of the conveyor system 10 may be easily performed from acentral location.

The logic circuitry necessary for the control system 48 to perform thevarious operations such as accumulation, slug release, and singulationrelease, may comprise a single integrated circuit 72 in the network card68, the integrated circuit 72 also providing the communication protocolwith the network cable 30. As used herein, logic circuitry should beconsidered to embrace discrete logic devices implementing logicalfunctions, programmable gate arrays and the like, and circuits such asmicroprocessors and microcontrollers executing a stored program. In thisregard, the integrated circuit 72 may handle low-level protocolsincluding timing, arbitration for the shared network cable and detectionof network errors and the like. As described in greater detailhereinafter, the control system 48 may comprise a single integratedprinted circuit board assembly having one or more of logic, I/O,communications, and power interfacing circuitry.

By investing the integrated circuit 72 with both communication protocoland control logic capabilities, the control system 48 may be extremelysimple providing for only basic motor and sensor control activitieswhile the logic of these operations is supported in the integratedcircuit 72. Nonvolatile memory within integrated circuit 72 allowsreconfiguration of the logic by commands from the central controller 34providing even greater configuration flexibility. After configuration bythe central controller 34, much of the communication on the networkcable 30 is peer to peer between control systems 48. The content of thiscommunication may be similar to that of the prior art, however, it willbe recognized that the data is communicated over the shared networkcable 30, thereby reducing wiring burden in the raceways 52.

In accordance with another aspect of the invention, the centralcontroller 34 may be eliminated or removed after configuration and thesystem may operate without the central controller 34 in a peer to peermode. Alternatively, a simple interface device may be attached in lieuof the central controller 34 to provide an indication of the operationof the system.

Another aspect of the invention provides for self-configuration of thecontrol systems 48 based on a network address (e.g., as set by addressswitch 70 or via programming commands). For instance, a first controlsystem 48 having a network address N may be adapted to automaticallyconfigure itself to receive a message from another control system 48having address N−1, which may be located upstream of the first controlsystem 48. In this regard, the control systems 48 may communicate witheach other in peer-to-peer fashion in order to share data, for example,to implement a conveyor control strategy such as singulation,accumulation, and the like. In addition, the first control system 48 maybe adapted to automatically configure itself on power up to send a datamessage to a third control system 48 at network address N+1, forexample, to indicate the status of the conveyor zone associated with thefirst control system 48 (e.g., object present, photoswitch on, etc.).Nevertheless, such peer-to-peer communication is not necessary and it ispossible to operate the present invention in a mode in which all sensorsignals are relayed to the central controller 34 and commands arereturned to the individual control systems 48, and no logic need beincluded or programmed on the control systems 48.

Referring again to FIG. 1, multiple network cables 30 may be connectedby a bridge 32 serving a number of different functions. The firstfunction of the bridge 32 is that of mapping redundant address spaces todifferent addresses so that limited address space protocols such as CANmay be expanded arbitrarily. Thus if addresses one through 128 are usedin each bank 24, the bridge 32 may concatenate a bank address to thoseaddresses thereby differentiating them. Bridge 32 also allowsinterconnection of network cables 30 in situations where astraightforward daisy chaining is difficult, for example, between banks24 or branches in the case of diverter conveyor sticks 26 which providea branching topology.

Referring to FIG. 5, according to another aspect of the invention, thecontrol systems 48 may be given insulation displacement type connectors74 such as allow for connection of the control system 48 to asemi-continuous ribbon cable 76. After mechanical connection of theconveyor sticks 12 into banks 24, the entire data connection of theconveyor sticks 12 may be handled by unreeling the ribbon cable alongthe raceways 52 and clamping it along its length beneath the insulationdisplacement connectors 74. Higher gauge power wiring may then be runand the connection process is complete.

Referring now to FIG. 7, an exemplary control system 48 is illustratedfor controlling a modular conveyor (e.g., conveyor stick 12) having amotorized roller 38 for moving objects (e.g., object 16) on the modularconveyor and an object sensor 42 for sensing objects 16 on the modularconveyor 12. The control system 48 comprises a drive controller 80adapted to control a motorized roller 38 in the modular conveyor 12, anda communications port 82 adapted to connect the control system 48 to anaddress-based network 30. The communications port 82 further providesfor sending outgoing addressed data (not shown) to other devices in thenetwork 30, and for receiving incoming addressed data from the network30.

The control system 48 further comprises a logic system 84 adapted toreceive an input signal from one of the object sensor 42 via one or moreinputs 86 and the communications port 82. The logic system 84 alsoprovides a roller control signal to the motorized roller 38 via drivecontroller 80 according to the input signal. According to another aspectof the invention, the control system 48 may further comprise one or moreoutputs 88, and the logic system 84 may include an output module (notshown).

As illustrated and described in greater detail hereinafter, the outputmodule may comprise a value source selector adapted to receive messagesfrom the address-based network 30, and a local logic function associatedwith the value source selector to create a binding, and to provide asignal thereto. One or more outputs 88 may receive an output value fromthe value source selector based on the signal from the local logicfunction in order to provide an output signal. The value source selectoris adapted to selectively ignore I/O and explicit messages from theaddress-based network 30 based on the binding, and to selectively use anidle action and set the output value according to an idle value when thelocal logic function is disabled. Such explicit messages may comprise,for example, configuration information, transferred data, messages toI/O ports, component fault or status information and requests for such,and the like, although it will be appreciated that the invention is notlimited to any specific form of such explicit messaging. In addition,the value source selector may selectively use a fault action and set theoutput value according to a fault value based on an override attribute,and selectively ignore idle messages according to the overrideattribute.

According to another aspect of the invention, the logic system 84 mayfurther comprise an indicator (not shown) adapted to receive messageinformation from the communications port 82 and providing indicatordata, as well as a logic unit receiving message information from thecommunications port 82, receiving indicator data from the indicator, andperforming a logic function. The logic unit may be adapted toselectively provide an output value to one or more of the outputs 88according to one of the message information and the logic function.

As illustrated and described in greater detail hereinafter, the logicsystem 84 may be further adapted to execute a stored program and toreceive a message from a master device via the communications port 82,wherein the message comprises a parameter (not shown). The logic system84 is further adapted to execute at least a portion of the storedprogram according to the parameter and to subsequently suspend executionof the stored program according to the parameter.

Many variations of the exemplary control system 48 may be implemented inaccordance with the present invention. For instance, the control system48 may, but need not, comprise the logic system 84, inputs 86 andoutputs 88, whereby the system 48 provides for start/stop and speedcontrol of the motorized roller 38 using the drive controller 80according to messaging from the network 30 via the communications port82. In another variation, the control system 48 may comprise the logicsystem 84, inputs 86, and outputs 88, whereby the system 48 may providestart/stop and speed control of the motorized roller 38 using the drivecontroller 80 according to messaging from the network 30 or according toprogrammable logic in the logic system 84. The inputs and outputs 86 and88, respectively, may thus be employed to perform control and/orinterlocking functions in addition to control of the roller 38 andreading of the objects sensor 42.

In another possible variation, the drive controller 80 may comprisevarious forms of motor control interface, including one or morecontactors, soft starters, and variable frequency drives. This variationmay or may not include inputs 86 and outputs 88, and may operate thedrive controller according to the logic system 84 or according tomessaging from the network 30. The invention may thus comprise anynumber of combinations of local logic, communications, inputs, outputs,and drive controllers, whereby the control system 48 may beadvantageously employed in any number of conveyor control applications.In this regard, it will be appreciated that all such variations of thecontrol system 48, including those not specifically illustrated anddescribed herein, are contemplated as falling within the scope of thepresent invention.

According to another aspect of the invention, the control system 48 maybe adapted to advantageously select an output value source for an outputdevice or module (e.g., outputs 88). This aspect of the invention avoidsthe problems associated with conventional output devices by allowing auser to define one or more attributes associated with the output device(e.g., drive controller 80 and/or outputs 88), as well as to define abinding to local logic (e.g., within the logic system 84). Thus, a usermay determine or select the output value source which will be used bythe output device under a variety of system conditions, depending onconfiguration of the output device or module, the current state of themodule, and the state of a network.

Referring now to the drawings, FIG. 8 illustrates a method 102 ofselecting an output value for an output device or module (not shown)according to the invention. The method may be employed in the controlsystem 48 of FIG. 7, for example, in order to select an output value forone or both of the drive controller 80 or the outputs 88. In thisregard, the method 102 may be implemented in the logic system 84 of thecontrol system 48. As discussed in greater detail infra, a user maydefine an association (e.g., a binding) between the output device and alogic function (not shown), which may comprise, for example, locallogic. With such an association defined, the output value update beginsat step 104, after which the presence of an explicit message isdetermined at step 106. Explicit messages may be a request to change theoutput value of the module or device, for example, a configurationrequest message.

If an explicit message has been received, the message will be ignored atstep 108 (e.g., the value in the explicit message will not be used toset the device output value), and an object state conflict error messagewill be returned at step 110 in response to the explicit message. Sincethe receipt of explicit messages as well as I/O messages discussedinfra, are generally asynchronous to the updating of the output value,the steps 106, 108, and 110, and the processing of I/O messages at steps112 and 114, are done without performing the set output value step 138.Thus, when an output has been associated with (e.g., bound to) a logicfunction, it no longer allows explicit messaging services to change itsvalue. Instead, it will return an error indicating an “Object StateConflict”.

Decision step 112 determines whether any I/O messages have beenreceived. If so, these are ignored at step 114, since the output deviceis associated with a logic function. As an example, an I/O message maybe sent by a PLC or other device which is running a ladder logicprogram, in order to update an output device according to the ladderlogic. When an output device is bound, it no longer uses the consumeddata from an I/O connection (e.g., with a PLC) to update its value.Instead, the source of information that it is bound to will be used.

During a normal update of the device output value, the presence offaults is determined at step 116. When an output is bound and a “ReceiveFault” event occurs or a consuming I/O connection times out, the outputdevice may override fault action and fault value settings, based on anoverride attribute (not shown) at step 118. If the override attribute isset, the method proceeds to step 120. If not, the output value is setaccording to a fault value at step 122. In this case, the device mayalso perform a fault action, which may comprise going to a known outputvalue (e.g., the fault value), or holding the last value, etc. Theoverride attribute, fault action, and fault value may be defined by auser via a network tool, as described in greater detail infra.

If no faults are present, or if the override attribute is set, step 120determines whether a force message has been received. A force messagemay be generated by a master on a network, which tells an output moduleto force an output to a specified state, regardless of the I/O statederived from a PLC logic program or from associated local logic. In someconventional systems, this is accomplished by a PLC receiving a forcemessage from the network, and ignoring it's own internal logic, insteadsending I/O messages to an output module based on the state specified inthe force message. Thus, the output will be set to the state specifiedin the force message until the module (or PLC) receives another messagefrom the master.

If such a force message has been received, step 124 determines whetherthe output force feature has been enabled. This feature may beimplemented via a force enable attribute (not shown). If the forcefeature is enabled, the device output value will be set according to aforce value at step 126. If no output force message is received, or ifthe force attribute is not enabled, the method proceeds to step 128,where the presence of an idle message is determined.

When an output is bound and a “Receive Idle” event occurs, the outputmay override idle action and idle value settings based on the setting ofan override attribute (not shown) at step 130, which may be the sameoverride attribute discussed supra with respect to fault override. Anexample of a receive idle event is where a user switches a PLC or otherprocessor from run mode into a program mode. Where the output isassociated with a logic function (e.g., being controlled locally), it isassumed that the I/O connection is not needed for controlling theoutput's value, and hence the invention provides for selectivelyignoring a receive idle event based on the override attribute. If anoutput is dependent on consumed data, the user can configure theoverride attribute accordingly. If the override attribute is not set, anidle action and idle value are used at step 132. The idle action may be,for example, to hold the last valid output value, or to go to a knownoutput value, such as the idle value. Otherwise, the method proceeds todecision step 134.

Step 134 determines whether the logic function (e.g., local logic) withwhich the output device has been associated has been disabled. If so,the idle action and idle value are used at step 132. When an output isbound, it will enter an idle state when local logic is disabled, duringwhich time idle action and idle values will be applied. If the locallogic is not disabled, the logic enabled output function is performed atstep 136, and the output value is set at step 138 according to the locallogic function, after which the value source selection method 102 iscompleted at step 140. The method illustrated in FIG. 8 thus allows auser many options in selecting an output value source for the outputdevice or module. This provides significant advantages over conventionalnetworked I/O where the output value is controlled by informationreceived from an I/O or explicit messaging service, or in the case of afault or idle condition, from fault state and idle state attributes,respectively.

Referring now to FIG. 9, a system 150 for selecting an output value 152for an output device or module 154 is illustrated, wherein the outputdevice 154 comprises an output value source selector 156 for determiningthe output value 152. The system 9, moreover, may be included in thelogic system 84 of the conveyor control system 48. The output valuesource selector 156 receives external signals from a network or othercommunications medium (not shown), including a fault/idle message 158, aforce message 160, an I/O message 162, and/or an explicit message 164.The device 154 may further comprise communication status and networkstatus override attributes 166 and 168, respectively. The output valuesource selector 156 may be bound to a function block 170 via a binding172. Although the exemplary system 150 is illustrated with the outputvalue source selector bound to function block 170, other bindings arepossible, such as a binding from the output value source selector 156 toinput 2 176. The binding 172 creates an association between the outputvalue source selector 156 and a logic function 186, such as the functionblock 170, which may include one or more hardware inputs 174, 176, and178, a hardware fault input 180, I/O messages 182, and/or explicitmessages 184. In this regard, outputs may be bound to function blocks,hardware inputs, faults, other outputs, or anything else a developerthinks may be useful in local logic 186.

Once the binding 172 has been made between the local logic 186 and theoutput value source selector 156 of the output device 154, I/O messages162 and explicit message 164 will be ignored. Fault and idle conditions158 may be selectively used or ignored based on the user-definedsettings of one or more override attributes including, for example,communication status override attribute 166. The logic functionperformed by the function block 170 will generally provide a value forthe output 152, unless the local logic 186 is disabled. In this case thedevice 154 enters an idle state, during which time an idle action andidle values (not shown) will be applied, for example, to go to a knownvalue (e.g., the idle value), or to hold the last value.

Referring now to FIG. 10, a system 200 is illustrated, which includesthe method and system for selecting an output value for an output deviceor module according to the present invention. A communications network202 is connected between several elements of the system 200, includingone or more computers 204 and 206, a programmable logic controller (PLC)208, and exemplary output modules 210 and 212. Modules 210 and 212 areillustrated as having direct access to the network 202. However, it willbe appreciated that the modules 210 and/or 212 may alternatively beconnected to a PLC or other processor via a backplane (not shown) with acommunications bus (not shown) thereon, with the PLC receiving messagesfor the module from the network 202. As an example, the PLC 208 may beconnected to one or more I/O modules 214, 216, and 218, respectively,which in turn provide outputs to, and/or receive inputs from a process220.

The exemplary output module 210 comprises a value source selector 222which may receive messages and/or signals from the network 202 as wellas a local logic function 224. An output 226 receives its value from thevalue source selector 222, and provides an output to a process 228. Aninputs unit 230 may measure one or more process variables from theprocess 228, which may be provided thereby to the local logic function224. The local logic function 224 may also be adapted to receive andsend messages via the network 202. The module 210 may further comprise aprocessor and a stored control program (not shown) for implementing oneor more control strategies to control the process 228. Similarly, themodule 212 includes a value source selector 240, an output 242, an input244, and a local logic function 246 to provide control of a process 248.

According to the invention, the value source selector 222 is adapted toselectively ignore I/O and explicit messages from the network 202 basedon the association with the local logic function 224 (e.g., binding),selectively use an idle action (not shown) and set the output value 226according to an idle value (not shown) when the local logic function 224is disabled, selectively use a fault action (not shown) and set theoutput value 226 according to a fault value (not shown) based on anoverride attribute (not shown), and selectively ignore idle messagesfrom the network 202 according to the override attribute. The module 210of FIG. 10 thus allows a user many options in selecting an output valuesource for the output 226. This provides significant advantages overconventional networked I/O where the output value is controlled byinformation received from an I/O or explicit messaging service, or inthe case of a fault or idle condition, from fault state and idle stateattributes, respectively.

Referring now to FIG. 11, an output device or module 250 is illustratedin which the methods and systems of the present invention may beimplemented. The module 250 comprises a processor 252 connected with amemory 254, and I/O section 256, and a network communications interface258. The interface 258 provides communications between the processor 252and a communications network 260. In accordance with the invention, anoutput of the I/O section 256 is associated with (e.g., bound to) alogic function, which may comprise a function block, a hardware input, afault, and/or an output. The logic function may be implemented in theprocessor 252 according to a program and/or user-defined attributesstored in the memory 254. Referring also to FIG. 12, the memory 254 maycontain one or more user-defined attributes associated with an outputvalue source selector feature of the module 250. The attributes mayinclude an idle action 270, an idle value 272, a fault action 274, afault value 276, and force enable attribute 278, and one or moreoverride attributes 280. The processor 252 may perform output valuesource selection according to the invention. These attributes and thevarious values (e.g., idle value, fault value, etc.) associated with anoutput device may be user-defined, for example, via a computer or othertool sending messages across the network 260, or even via dipswitches onthe output device.

Referring also to FIG. 8, the module 250 may comprise instructions (notshown) in the memory 254 for implementing the output value sourceselection method 102, by which an output value may be determined by theprocessor 252 for an output of the I/O section 256. In this regard, theassociation (e.g., binding) of an output to a logic function allows auser to define where the output will get its output value from, based onthe configuration of the module 250, the state of the module 250, andthe state of the network 260, as discussed supra with respect to FIGS. 8and 9. In this regard, the processor or output value source selector 252may be adapted to selectively ignore I/O and explicit messages from thenetwork 260 based on the association between the output and local logic,selectively use an idle action and set the output value according to anidle value when the local logic function is disabled, selectively use afault action and set the output value according to a fault value basedon an override attribute, and selectively ignore idle messages from thenetwork 260 according to the override attribute.

Another aspect of the invention provides a method and apparatus forproviding an output value in an output device, which may be employed inthe control system 48 for operation of a conveyor system 10. This aspectof the invention allows a user to define a logic function and toassociate the logic function with one or more status/event indicators.The logic function then provides an output value to the device outputaccording to the status/event indicators as well as the logic program.This may determine, for example, whether the output value is based on anI/O message received by the device from a network, or based on thelogic. As opposed to conventional conveyor control methods andapparatus, the present invention allows a user to define output devicebehavior in a variety of circumstances, thereby providing significantlyimproved design flexibility.

FIG. 13 illustrates a method 302 of providing an output value for anoutput device in a conveyor control system. An output is associated witha logic function at step 304 and the logic function is associated withone or more status/event indicators at step 306. As discussed in greaterdetail hereinafter, the logic function may comprise one or more functionblocks, for example, boolean operators, bi-stable functions (e.g.,flip-flops), counters, timers, analog functions, etc. The association ofthe logic function with the indicator at step 306 may be a logicalconnection (e.g., a binding) in an output module, which a user mayaccomplish via a configuration tool through a network, as discussed ingreater detail infra. The method also comprises receiving status andvalue messages from the network at steps 308 and 310, respectively,after which the status/event indicators are updated at step 312according to information received in the status message and furtheraccording to the status of the output device.

It will be appreciated that a single network message may include bothvalue and status information. In this regard, the network message mayinclude indications of the status of various network devices, forinstance, network status, devices status of other modules, etc. Themessage may also include information about the occurrence of variousevents, such as faults and the like. In this way, the method maintainssituation awareness of a variety of status/event conditions in adistributed control system, which may be taken into account indetermining an output value for the output module or device.

The status/event indicator may comprise, for example, a list or table incontrol system memory, whereby a processor in the system may update theinformation upon receipt of network message, and may access theinformation in determining an output value in accordance with the userdefined logic function. At step 314, the logic function is executed,wherein the associated status/event indications are consulted indetermining an output value for the device. Thereafter, the logicfunction provides an output value to the output at step 316. The logicitself may compute or derive the output value, or the value may beobtained from a network value message (e.g., a typical I/O message),depending on the logic function. Since the logic function itself may beconfigured to account for one or more of the status/event indications inthe indicator, the determination of the output value according to themethod 302 provides numerous options for a user in defining the outputdevice behavior. Optionally, a network message may be sent at step 318according to the logic function and/or the indicator. For example, wherean event (e.g., a fault) causes the output value to be derived from thelogic function instead of from an I/O message, a user may wish toinitiate a network message telling other devices on the network that theoutput device is changing its control strategy because of the fault.

The method 302, thus allows significantly improved flexibility indefining or configuring distributed conveyor control system elements.The method allows the conveyor control system 48 to be aware of its ownsituation (e.g., status) as well as the status of other devices on anetwork and of the occurrence of various events in the system. Theseindications are associated (e.g., linked or bound) with a user-definedlogic function, which accounts for these indications in determining theoutput value for the device.

Referring now to FIG. 14, a system 350 and output device 352 areillustrated, wherein the device 352 is provided with a logic function354 associated with one or more status/event indicators 356, an output358, and a network interface 360. The network interface 360 transmitsand receives information to and from a network 362, in the form ofmessages. The messages may be value messages and/or status messages, orthe messages may each include both value and status information. Thestatus/event indicators 356 are likewise associated with the network,and thus may receive updated status and/or event information fromnetwork messages. The logic function 354 selectively provides an outputvalue to the output 358, which in turn provides an output signal (notshown) to a process 364 (e.g., a conveyor motorized roller). By takinginto account the status/event indicators 356, the logic function 354provides the ability to define the behavior of the output 358 in avariety of situations which was not heretofore possible.

The logic function 354 and the association thereof with the status/eventindicators 356 in device 352 may be configured via a configuration tool66 connected to the network 362. For example, a user may define thelogic function 354 in terms of various function blocks (e.g., booleanoperators, flip-flops, counters, timers, etc.) and create an associationbetween the logic function 354 and the status/event indicators 356 usingthe tool 366, which may be a computer, workstation, etc. Theconfiguration (not shown) may then be sent by the configuration tool 366to the output device 352 via one or more messages on the network 362.

FIG. 15 illustrates further aspects of the present invention, wherein anoutput device 400 has an output 402 for providing an output signal (notshown) to a process 404, such as a motorized conveyor roller assembly.The device 400 also comprises a communications or network interface 406providing for transmission and/or receipt of messages to and from anetwork 408. A processor 410 interfaces with the network interface 406along with a memory 412 and the output 402. In addition, the device 400may include one or more inputs 414 for measuring various parameters orvariables associated with the process 404. In this regard, the device400 may be an I/O module, which may be integrated into or otherwiseassociated with the conveyor control system 48. The network 408 mayprovide communications between the device 400 and one or more otherdevices connected thereto, such as computers, workstations, other I/Omodules, PLCs, and the like (not shown), in order to form a distributedcontrol system. It will be appreciated that the output device 400 mayalternatively be connected to other communications mediums, such as, forexample a backplane communications bus, and the like, within the scopeof the invention.

In this regard, the output device 400 may receive I/O or other types ofmessages from a master (e.g., a PLC) via the network 408 (or othercommunications medium) and the network interface 406. These messages mayinclude value and/or status information which are used to update one ormore status/event indicators 416 in the memory 412, and/or to provide anoutput value to the output 402. A user-defined logic function 418 mayalso reside in the memory 412 for determining an output value for theoutput 402 according to one or more of the status/event indicators 416.

According to another aspect of the invention, the logic function may beperformed or executed by the processor 410 according to programinstructions (not shown) within the memory 412. In addition, theprocessor may update the status/event indicators 416 in the memory 412according to messages (not shown) received from other network devicesvia the network 408 and interface 406. The configuration or definitionof the logic function 418 as well as the association thereof with one ormore of the status/event indicators 416, may be performed by a user viaa configuration tool (not shown) through the network 408 and interface406. The association between the indicators 416 and the logic function418 may comprise, for example, a binding or linking, whereby the outputvalue determination takes the indicators into account. As discussed ingreater detail infra, the logic function 418 may be defined in terms ofone or more function blocks (not shown), whereby a user may configurelogical or other functions (e.g., boolean operations, flip-flops, timer,counters, and the like) in order to provide an output value (not shown)to the output 402. The logic function 418 may alternatively beimplemented be circuitry or components (not shown) other than theprocessor 410, which may be adapted to provide an output value to theoutput 402. The behavior of the output 402 may therefore be defined in avariety of event/status situations, providing the user with significantdesign flexibility not otherwise possible with conventional devices.

Referring now to FIG. 16, several aspects of the present invention areillustrated in which an output device 500 comprises an output 502providing an output signal 504 to a process 506 (e.g., conveyor system10) according to an output value 508 determined by an exemplary logicfunction 510. The logic function 510 is illustrated as comprising alogical function block 512 (inverter), a function 514 (A), a function516 (B), and a function block 518 (OR), with the output of the ORfunction block 518 providing the output value 508 to the output 502. Itwill be noted that logic function 510 may comprise function blocks(e.g., 512, 518) as well as other functions (e.g., 514, 516).

The inputs of function block 518 are connected to the outputs offunctions 514 and 516. The inverter function block 512 and the function514, are associated with (e.g., bound to) an I/O connection healthstatus/event indicator 520 via a binding 522, with the inverter functionblock 512 providing a signal to the input of function 516. The indicator520 is one element in a status/event indicator table or list 524 whichfurther includes a message connection health indicator 526, an I/O errorindicator 528, a run/idle indicator 530, a network error indicator 532,an I/O point fault indicator 534, a hardware input indicator 536, ahardware output indicator 538, an I/O data indicator 540, and an outputdevice status indicator 542. It will be appreciated that thestatus/event indicator list 524 may comprise any number of indicatorsrelated to system and/or module status or event information, and is notlimited to those illustrated in FIG. 16.

A network interface 544 provides communication capabilities between theoutput device 500 and a network 546, and may be operatively connected tothe status/event indicator list-524 as well as a message buffer 548. Asillustrated, the output device 500 may provide an output value 508according to the logic function 510, based on one or more entries in thestatus/event indicator list 524. In this way, the behavior of the output502 may be defined by a user, taking into account the status of anydevice in a control system, including the status 542 of the outputdevice 500. In the exemplary configuration of FIG. 16, a safetyapplication is illustrated in which control of the output 502 isswitched between the functions A 514 and B 516 depending on the healthof an I/O connection from a master (not shown), as indicated by thestatus/event indicator 520.

If the connection is healthy, function A 514 controls the output, forexample, by providing the output value 508 according to an I/O message(not shown) received from the network 546 via the interface 544, andprovided to function A 514 of the logic function 510 from the messagebuffer 548. If the I/O connection with the master is faulted, the I/Oconnection health indicator 520 in list 524 is updated by the networkinterface 544, and the binding 522 between indicator 520 and logicfunction 510 causes function B 516 to provide an output value 508 to theoutput 502 via the OR function block 518.

The function B 516, for example, may implement a controlled shut down ofthe process 506 due to the I/O connection health fault associated withthe master. In addition, the occurrence of such a fault may beconfigured by a user to trigger transmission of a message to the network546 via the message buffer 548 and the network interface 544. This maybe accomplished in the definition of the logic function 510 by, forexample, linking the output of the inverter function block 512 to themessage buffer 548 as illustrated in FIG. 16. In this way, the outputdevice 500 may be configured to perform a controlled shutdown of theprocess 506 according to the event status indicator 520, and tobroadcast a message across the network 546 informing one or more devicesthereon that a controlled shutdown of the process 506 is underway.

Many different configurations of functions are possible within the scopeof the invention, including those not specifically illustrated in thedrawings. In addition, many different functions are possible, includingbut not limited to boolean operators, flip-flops, counters, timers,analog functions, and the like.

Referring now to FIG. 17, another exemplary application of the presentinvention is illustrated wherein an output device 600 comprises anoutput 602 providing an output signal 604 to a process 606 according toan output value 608 from a logic unit 610. The logic unit 610 isassociated with a list 624 of status/event indicators which comprises anI/O connection health indicator 620, a message connection healthindicator 626, an I/O error indicator 628, a run/idle indicator 630, anetwork error indicator 632, an I/O point fault indicator 634, ahardware input indicator 636, a hardware output indicator 638, an I/Odata indicator 640, and an output device status indicator 642. Theassociation between the event/status indicator list 624 and the logicunit 610 comprises a binding 622 which provides an input to the logicunit 610 from the I/O point fault indicator 634. The entries in thestatus/event indicator list 624 are updated by a network interface 644according to one or more messages (not shown) from a network 646, whichmay include, for example, network I/O messages, network status messages,network value messages, etc.

A message buffer 648 provides for transmission and receipt of networkmessages from and to the logic unit 610. Referring also to FIG. 18,various aspects of the invention are illustrated in an exemplaryredundancy application. In this example, two input devices 650 and 652feed the output device 600, which provides an output signal 604 to theprocess 606 based thereon. The output device 600 may receive the values660 and 662, respectively, of the input devices 650 and 652, forexample, from the message buffer 648. This may be the case where one ormore separate input modules (not shown) on the network 646 provide thevalues 660 and/or 662. Where the output device 600 is an I/O module, theinputs may be part of the device 600.

The logic unit 610 of output device 600 compares the two input values660 and 662 before making any decisions. If one of the input devices 650or 652 were to fail (e.g., device 652), the output device 600 couldcontinue to operate using only input device 650, according to the userdefined configuration of the logic unit 610. The failure of an input inthis example may be determined according to the I/O point faultindicator 634. The output device 600 can further be configured to send amessage 670 from the logic unit 610 to another device (not shown) on thenetwork 646, via buffer 648 and interface 644, to indicate that a faulthas occurred in one of the input devices 650 and/or 652.

Furthermore, the logic unit 600 could be configured to continueoperation according to one of the redundant input devices 650 or 652 fora predetermined time period after sending the message. In this case, themessage 670 could include information that an input device has failed,and the output device 600 will continue to operate according to a singleremaining input device for a specified time period. After the timeperiod has expired, the logic unit 610 may be configured, for example,to perform a controlled shut down of the process 606. The output device600 can thus notify a master controller (e.g., a PLC on the network646), via message 670, that input device 652 has failed, and thatoperation with device 650 will continue for a configurable time period.This allows, for example, time for the failed device to be replacedwithout stopping the process.

It will be appreciated that many configurations and output devicebehaviors are possible according to the invention, and that theinvention is not limited to those illustrated and described herein. Forinstance, many different logical functions may be implemented byconfiguring one or more logical function blocks with associations to oneor more status/event indicators. In this regard, the function blocks maybe boolean operators, flip-flops, counters, timers, etc., and may alsoinclude analog functions within the scope of the present invention.

Another aspect of the invention provides a system and methodology bywhich a user can perform single step and/or time sliced operation of oneor more control systems 48 devices in a distributed conveyor system(e.g., system 10). The user may then perform system diagnostics, forexample, by interrogating certain control systems 48 to obtain statusinformation, output and input values, and the like. The system may thenbe further iterated and the method repeated, thus allowing theidentification of logic programming and/or hardware problems in asystem. The system and methodology of the present invention therebyprovides for significantly improved diagnostic and troubleshootingcapabilities over conventional conveyor control systems.

Referring now to FIG. 19, an exemplary distributed control system 100 isillustrated in which various aspects of the present invention may beimplemented. The system 700 includes a network 702 interconnectingcomputers 704, 706, PLC 708, and control devices 710 and 712 forcommunication therebetween. The PLC 708 may be installed in a rack (notshown) along with one or more I/O modules 714A, 714B, and 714C, by whichthe PLC may communicate with the modules (hereinafter collectivelyreferred to as 714) via a bus or other communications medium (notshown). In this manner, the PLC 708 may control a process 716 via theI/O modules 714, which may or may not directly communicate with thenetwork 702.

The control devices 710 and 712 may be controllers, smart I/O modules,and/or conveyor control systems, respectively, for controlling and/orinterfacing with processes 720 and 722, respectively (e.g., conveyorzones 36). Device 710 comprises a network interface 724 providingcommunications between a microprocessor 726 and the network 702.Microprocessor 726 is further connected to a memory 728, an input stage730, and an output 732. The memory 728 may store a control program (notshown) and data related to the process 720, for example, an I/O table(not shown). The input stage 730 and the output 732 provide interfacesbetween the device 710 and the process 720. Similarly, device 712comprises a network interface 734 providing communications between amicroprocessor 736 and the network 702. Microprocessor 736 is furtherconnected to a memory 738, an input stage 740, and an output 742. Theinput stage 740 and the output 742 provide interfaces between the device712 and the process 722.

In accordance with the present invention, the devices 710 and/or 712 mayreceive a message (not shown) from the network communications medium702, wherein the message includes a parameter, execute at least aportion of the stored control program (not shown) according to themessage parameter, and subsequently suspend or stop execution of thestored program according to the parameter. The message may put thedevices 710 and/or 712 into a step mode, or may cause execution of atleast a portion of the program in the devices 710 and/or 712, which isalready in a step mode by virtue of, for example, a previous mode changemessage. The invention thus allows a user to begin execution of acontrol device program or internal logic for a limited or specified timeperiod or number of logic iterations, after which the devices 710 and/or712 will suspend execution.

Referring also to FIG. 20, an exemplary mode change message 750 inaccordance with the invention is illustrated having a module addressfield 752, a message type field 754, and an instruction field 756instructing the recipient control device (e.g., devices 710 and/or 712)to change mode to step mode. Following receipt of a mode change message750, the devices 710 and/or 712 may suspend execution of theirrespective stored control programs (not shown) and await another modechange message or a step command message as described in greater detailinfra. As is understood in the art, the microprocessors 726 and 736 ofdevices 710 and 712, respectively, receive messages from the network 702via the network interfaces 724 and 734, respectively.

FIG. 21 illustrates an exemplary step command message 760 in accordancewith the invention, which comprises a module address 762, a message typefield 764 indicating the type as a step command, a step type 766, and astep parameter 768. The step type 766 may comprise, for example, anindication of whether the desired step is a timed step or an iterationstep. The corresponding step parameter 768 may comprise, for example, anumber of iterations or a step time value, depending on the step type766. As described in greater detail hereinafter, one or more controldevices (e.g., devices 710 and/or 712) may execute a portion of theirrespective stored control programs (not shown) according to the steptype 766 and the step parameter 768 upon receipt of the message 760 viathe network 702 or other communications medium.

Referring now to FIG. 22, another exemplary mode change message 770 isillustrated having a module address field 772, a message type field 774,and an instruction field 776 instructing the recipient control device(e.g., devices 710 and/or 712) to change mode to the previous mode.Following receipt of such a mode change message 770, the devices 710and/or 712 may return to execute mode and resume execution of theirrespective stored programs (not shown) after being in the step mode.

FIGS. 23 and 24 illustrate an exemplary method 800 of performing afunction in a control system in accordance with the present invention.The method 800 begins at step 802 where a mode change message (e.g.,message 750 of FIG. 20) is received, after which program execution issuspended or stopped at step 804. Thereafter, the device waits for astep command message at steps 806 and 808. As will be appreciated fromthe discussion of FIGS. 27 through 29 infra, a single message maycomprise both a mode change command and a step command in accordancewith the invention. It will be further appreciated that messages otherthan step command type messages may be received at this point (e.g., I/Omessages, other mode change messages, etc.), which may be operated onand/or responded to accordingly. However, for the sake of brevity, themethod 800 is illustrated in FIG. 23 as waiting for a step commandmessage via steps 806 and 808.

Once a step command has been received, the step type and parameter areobtained therefrom at step 810. Decision step 812 then determineswhether the step type is timed or iterations. If the step type is timedstep, the device (e.g., device 710 and/or 712) executes its storedcontrol program according to the time specified by the step time valueparameter at step 814 before program execution is suspended or stoppedat step 816. Alternatively, if the step type is iterations at step 812,the device executes the number of program iterations according to thestep parameter at step 818 before program execution is stopped orsuspended at step 816.

Referring also to FIG. 24, once program execution has been stopped orsuspended at step 816, the control device waits for receipt of anothermessage at steps 818 and 820. Once a message has been received from thecommunications medium (e.g., network 702), the message type isdetermined at decision step 822. If the message is a step command, thedevice obtains the step type and parameter from the message at step 810of FIG. 23 as discussed supra.

If the new message is not a step command or mode change type message(e.g., I/O or other explicit message), the device provides data and/orstatus information, or otherwise responds to the message at step 824,before returning to step 818 to await another message. In this regard,data may be provided by a device such as device 710 of FIG. 19, via amessage (not shown) on the network 702 to a device (e.g., computer 704)which requested the data. In this manner, a user may generate stepmessages from a computer 704, and when the device 710 has completed stepmode execution and stopped, data values and/or status information may beobtained from the device 710 via I/O or other explicit messaging.Returning to FIG. 24, if the new message is a mode change message, thedevice will change mode according to the new mode change message at step826 and resume program execution according to the new mode at step 828.

In accordance with another aspect of the invention, step parameters maybe provided to a distributed control device in a separate message.Referring now to FIG. 25, an exemplary step parameter message 900 isillustrated, having a module address 902, a message type 904 indicatinga step parameter message, a step type 906 indicating iteration or timedstep as described supra, and a step parameter 908 corresponding with thestep type 906 and indicating a number of iterations or a step timevalue, respectively. This form of message provides step parameters to adevice (e.g., device 710 and/or 712), for example, where a prior modechange message (e.g., message 750 of FIG. 20) has placed a controldevice (e.g., device 710 and/or 712 of FIG. 19) into step mode.

Referring also to FIG. 26, another exemplary step command message 910 isillustrated having a module address 912 and a step command message type914. This message may be used to initiate a step of a device inaccordance with the invention, where, for example, the device has beenprovided with a step type 906 and a step parameter 908 via a previousstep parameter message 900 such as that illustrated in FIG. 25 anddescribed supra. Many different message protocols are possible,including those not specifically illustrated in the figures, which fallwithin the scope of the present invention.

Referring now to FIGS. 27-29, another exemplary method 1000 ofperforming a function in a control system or device is illustrated inaccordance with the invention. A change mode message is received at step1002, after which execution of the program stored in the control deviceis stopped or suspended at step 1004. Thereafter the device waits for astep parameter message at steps 1006 and 1008. It will be furtherappreciated that messages other than step parameter type messages may bereceived at this point (e.g., I/O messages, other mode change messages,etc.), which may be operated on and/or responded to accordingly.However, for the sake of brevity, the method 1000 is illustrated in FIG.27 as waiting for a step parameter type message via steps 1006 and 1008.

Once a step parameter message (e.g. message 900 of FIG. 25) is receivedat step 1008, the step type and parameter are obtained therefrom at step1010. The device then waits for receipt of another message at steps 1012and 1014 (FIG. 28).

Upon receipt of a message at step 1014, decision step 1016 determinesthe message type. If the message is a step command message, the stepcommand is executed as described in greater detail infra and illustratedin FIG. 29. If the message is a change mode message, the device changesmode according to the mode change message at step 1020, after whichprogram execution is resumed according to the new mode at step 1022. Ifthe new message is not a step command or mode change type message (e.g.,I/O or other explicit message), the device (e.g., device 710 and/or 712)provides status information and/or data (e.g., via a network message tothe requestor), or otherwise responds to the message at step 1024, andreturns to step 1012 to await further messages.

Referring now to FIG. 29, if the message received at step 1014 is a stepcommand type message, the device determines whether the step type (e.g.,step type 906 of FIG. 25) is timed or iteration at step 430. If the steptype is timed step, the device (e.g., device 710 and/or 712) executesits stored control program according to the time specified by the steptime value parameter at step 1032 before program execution is suspendedor stopped at step 1034. Alternatively, if the step type is iterationsat step 1030, the device executes the number of program iterationsaccording to the step parameter at step 1036 before program execution isstopped or suspended at step 1034. Once the program has been stepped(e.g., timed step via step 1032 or iteration stepped via step 1036), andthe program execution has again been stopped or suspended at step 1034,the device again waits for a message at step 1012 of FIG. 28. Thus, auser may perform stepped execution of the control or logic programstored in the device, and obtain process or other information from thedevice at step 1024 via I/O or other explicit messages while the programexecution is suspended. Proceeding in this fashion, a user mayadvantageously troubleshoot system programming and other errors inwidely distributed control systems.

It will be recognized that more than one device (e.g., devices 710and/or 712) may be placed into step mode and respond to step commands,etc., via a single message. In this way, a user can synchronize singlesteps of distributed control system execution with a single networkmessage. For example, a user may send a message from computer 704 inFIG. 19 to PLC 708, device 710 and device 712 to perform a specifiedtime period of execution of the programs stored therein. Thereafter,data relating to the controlled processes 716, 720, and/or 722,respectively, can be obtained from the devices 708, 710, and/or 712while the execution of these programs is stopped or suspended. Thismethod or process can be repeated any number of times in order tofacilitate the identification of problems and/or programming errors inthe system hardware, logic programs, actuators, etc. In addition,different devices (e.g., devices 708, 710, and/or 712) may be sentdifferent step parameters via a number of addressed step parametermessages, and then started via a single broadcast step command message.The present invention thus provides powerful diagnostic and debuggingmethods particularly applicable to widely distributed control systems.It will be further recognized that many message protocols are possiblewithin the scope of the invention, beyond those illustrated anddescribed herein.

Although the invention has been shown and described with respect tocertain illustrated aspects, it will be appreciated that equivalentalterations and modifications will occur to others skilled in the artupon the reading and understanding of this specification and the annexeddrawings. In particular regard to the various functions performed by theabove described components (assemblies, devices, circuits, systems,etc.), the terms (including a reference to a “means”) used to describesuch components are intended to correspond, unless otherwise indicated,to any component which performs the specified function of the describedcomponent (i.e., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure, which performs thefunction in the herein illustrated exemplary aspects of the invention.In this regard, it will also be recognized that the invention includes asystem as well as a computer-readable medium having computer-executableinstructions for performing the steps of the various methods of theinvention.

In addition, while a particular feature of the invention may have beendisclosed with respect to only one of several implementations, suchfeature may be combined with one or more other features of the otherimplementations as may be desired and advantageous for any given orparticular application. Furthermore, to the extent that the terms“includes”, “including”, “has”, “having”, and variants thereof are usedin either the detailed description or the claims, these terms areintended to be inclusive in a manner similar to the term “comprising.”

1. A modular conveyor network system comprising: a plurality of conveyorunits connected there together in a network; and a control systemassociated with each conveyor unit, the control system comprising anoutput module to control an output device based on network messagesand/or a local logic function.
 2. The system of claim 1, the outputmodule comprising a value source selector to receive and send messagesto and from the network.
 3. The system of claim 2, wherein the sourceselector is associated with the logic function to create a binding. 4.The system of claim 3, wherein the source selector can be configured toignore I/O and explicit messages from the network based on the binding.5. The system of claim 4, wherein explicit messages include one ofconfiguration information, transferred data, messages to I/O ports,component fault information, and requests.
 6. The system of claim 4,wherein the selector can utilize a fault action and set an output valuein accordance with a stored fault value based on an override attribute.7. The system of claim 6, wherein the selector can selectively ignoremessages in accordance with the override attribute.
 8. The system ofclaim 6, wherein a user defines the override attribute.
 9. The system ofclaim 4, the output module further comprising an input unit to measureone or more process variables and provide them to the logic function.10. The system of claim 9, wherein the process variables correspond tostatus or event indicators related to the conveyor system.
 11. Thesystem of claim 1, wherein the output module comprises a processor and astored control program to implement one or more control strategies. 12.The system of claim 11, wherein the control program employs user definedattributes including at least one of idle action, idle value, faultaction, fault value, force enable attribute and override attribute. 13.The system of claim 1, the logic function including one or morefunctions blocks including, Boolean operators, bi-stable functions,counters, timers and/or analog functions.
 14. The system of claim 1,wherein the output device is a belt drive controller.
 15. A modularconveyor system comprising: a plurality of conveyor units connectedtogether via a network to facilitate implementation of a controlstrategy; a means for enabling control systems associated with eachconveyor unit to select amongst several output sources providing outputto a conveyor drive controller.
 16. The system of claim 15, wherein themeans for selecting output sources includes a selector component thatgenerates output based on a binding associated with a logic function.17. The system of claim 16, wherein the selector component ignorescontrol information received from an I/O or explicit message service.18. A modular control system methodology for providing an output valueto a driver controller including: receiving a binding defined by a userbetween a controller and a logic function; ignoring explicit messagesand I/O messages received from a conveyor network; and setting theoutput value in accordance with the logic function.
 19. The method ofclaim 18, further comprising detecting the presence of a fault andsetting the output value according to stored fault value settings unlessan override attribute is set.
 20. The method of claim 19, furthercomprising receiving a force message from a master controller andsetting the output value to the supplied force value if a output forcefeature has been enabled.